Field of the Invention (Technical Field)
The present invention relates to a weighing device, and specifically a weighing device that can be used to measure the weight of powder in blister packs.
Description of Related Art
Pharmaceutical powder products are often provided in blister packs, formed of a moulded plastic strip and covered with a foil or paper capping material. These blister packs are typically filled in a production line and a powder dispensing head is configured to provide a particular dose of powder into an individual blister or receptacle. The blisters or receptacles are then covered with the capping material.
It is of fundamental importance that the dispensing head provides a precise dose of powder to each receptacle. Any error in the dose could contravene regulatory requirements and/or put a patient's health in jeopardy.
In-line techniques for measuring the weight of powder in blister packs typically involve measuring the weight of blister packs during the manufacturing process, and then subtracting the assumed weight of the packaging material. In these techniques a load measuring device is typically provided to measure the weight of blister packs as they are translated horizontally in a manufacturing assembly. A problem with many in-line techniques is that the accuracy of weight measurements is reduced when the measurements are performed at speed. In addition, any errors in the assumed weight of packaging will have an adverse effect on the accuracy of any conclusions for the weight of powder.
Off-line techniques for measuring the weight of powder in blister packs typically involve an analysis at the end of a manufacturing run. Typically an individual blister strip is selected and weighed, and the results for this blister strip are assumed to be indicative of all blister strips produced in the manufacturing run. An example off-line measurement technique is described in EP 1449767. In this document a technique is described whereby a powder filled blister is punched from a blister strip without breaking the blister. The punched blister is then weighed, and the weight of the powder is determined by subtracting the assumed weight of the packaging material. It would be desirable to have an off-line technique that can measure the weight of powder in blisters that cannot be easily separated from a strip using a punching process. Another limitation of the technique described in EP 1449767 is that there may be inaccuracies in the assumed weight of packaging in a punched blister and there may be inconsistencies in the weight of packaging included each time a blister is punched from a strip.